It is often desirable to seal the opening of a container using a removable or peelable seal, sealing member, or inner seal. Often a cap or other closure is then screwed or placed over the container opening capturing the sealing member therein. In use, a consumer typically removes the cap or other closure to gain access to the sealing member and then removes or otherwise peels the seal from the container in order to dispense or gain access to its contents.
Initial attempts at sealing a container opening utilized an induction- or conduction-type inner seal covering the container's opening where the seal generally conformed to the shape of the opening such that a circular container opening was sealed with a round disk approximately the same size as the opening. These prior seals commonly had a lower heat activated sealing layer to secure a periphery of the seal to a rim or other upper surface surrounding the container's opening. Upon exposing the seal to heat, the lower layer bonded to the container's rim. In many cases, these seals included a foil layer capable of forming induction heat to activate the lower heat seal layer. These prior seals tended to provide good sealing, but were often difficult for a consumer to remove because there was nothing for the consumer to grab onto in order to remove the seal. Often, the consumer needed to pick at the seal's edge with a fingernail because there was little or no seal material to grasp.
Other types of seals for containers include a side tab or other flange that extended outwardly from a peripheral edge of the seal. These side tabs are generally not secured to the container rim and provide a grasping surface for a consumer to hold and peel off the seal. These side tabs, however, extend over the side of the container rim and often protrude into a threaded portion of the closure. If the side tab is too large, this configuration may negatively affect the ability of the seal to form a good heat seal. The side tabs (and often the seal itself) can be deformed or wrinkled when the closure or other cap is placed on the container due to contact between the closure (and threads thereof) and tabbed part of the seal. To minimize these concerns, the side tabs are often very small; thus, providing little surface area or material for a consumer to grasp in order to remove the seal.
Yet other types of seals include a sealing member having a tab defined on the top of the seal. One approach of these prior seals includes a partial layer of coated pressure sensitive adhesive to secure the tab to a layer of metal foil. The tab was formed by a full layer extending across the entire surface of the sealing member, but the full layer was only bonded to half of the seal to form the tab. This type of top-tabbed seal offered the advantage of a larger tab, which provided more grasping area for the consumer to hold and peel off the seal, but required a full additional layer of material in order to form the tab. In other approaches, the seal may include a tab formed from the additional full layer of film combined with an additional full layer of adhesive utilizing a part paper or part polymer layer, called a tab stock, to form the tab. This part layer is inserted between the additional full layer of adhesive and lower seal portions to prevent the tab from sticking to the layers below, which formed the tab. In all the prior types of top-tabbed-like seals, the gripping tab was formed by a full layer of material (or a full layer of material and a full layer of adhesive) that extended across the entire surface of the seal.
As mentioned above, a cap or other closure is typically screwed or otherwise secured to a finish or neck of a container. This captures the sealing member between the top of the cap and container rim. In many instances, the cap has an annular bead or downwardly protruding ring (sometimes called a bead line) on the underside of its top inner surface. This annular bead is sized and positioned to generally correspond with an upper land area of the container rim when the cap is secured to the container. This annular bead helps provide pressure to secure the sealing member to the rim land area. However, many of the prior sealing members included a foam layer to provide insulation from heat generated during the heat sealing process. In some cases, there can be problems with the foam layer interacting with the cap annular bead during the cap sealing process. Heat from the cap sealing process combined with the focused downward pressure from the annular bead on the foam layer in the sealing member can damage or result in deterioration of the foam layer in the areas above the container rim. In extreme cases, the foam may melt or air cells in the foam may collapse. This shortcoming is more prevalent when the cap sealing process is over sealed (that it, when too much heat is applied or heat is applied for too long during the cap sealing process).
This melting and/or cell collapse may result in exposure of the metal foil or other polymer layers below the foam at the peripheral areas of the sealing member. In some cases, when the consumer lifts up the tab to remove the sealing member, the consumer is presented with an unsightly seal having an uneven foam layer under the tab with intact center portions of foam and melted or damaged edge portions of the foam. In extreme cases, the outer peripheral portions of the foam may melt completely, which exposes the metal foil or other layers under the tab.